1. Field of the Invention
The present invention relates to preforming and duplicating operations on lapidary machines, and more particularly to the grinding of cabochons from stone blanks.
2. Description of the Prior Art
The forming of a cabochon from a rough stone blank involves grinding the blank to the desired peripheral size and shape and with a selected bezel angle, and then grinding the face of the blank to the desired domed curvature. In the past the first of these steps was performed by free-hand holding the blank against a rotary grinding surface and grinding the blank to a perimeter line marked on the stone by reference to a selected template, or by use of a duplicator having special templates. Heretofore such a duplicator has operated with the stone blank arranged with its plane coinciding with the plane of the grinding wheel, and hence, when the cabochon is to be oval shaped the point of grinding contact between the periphery of the grinding wheel and the periphery of the stone blank varies as the blank is turned to progressively expose its periphery to the grinding surface. As a consequence, the duplicator template must be compensated in shape from the oval desired for the cabochon, and this means that a special template is required for each size and shape of cabochon.
Automatic cabochon grinding machines have been developed to form both the periphery and domed curvature of a cabochon, but these machines require use of a special diamond faced wheel concavely shaped at its periphery in conformance with a quadrant of the particular cabochon to be formed. These machines are relatively expensive and require a respective special grinding wheel for each cabochon size and shape.